Plants are subjected to fluctuations in light intensity, and this might cause unbalanced photosynthetic electron fluxes and overproduction of reactive oxygen species (ROS). Electrons needed for ROS detoxification are drawn, at least partially, from the cellular glutathione (GSH) pool via the ascorbate-glutathione cycle. Here, we explore the dynamics of the chloroplastic glutathione redox potential (chl-EGSH) using high-temporal-resolution monitoring of Arabidopsis (Arabidopsis thaliana) lines expressing the reduction-oxidation sensitive green fluorescent protein 2 (roGFP2) in chloroplasts. This was carried out over several days under dynamic environmental conditions and in correlation with PSII operating efficiency. Peaks in chl-EGSH oxidation during dark-to-light and light-to-dark transitions were observed. Increasing light intensities triggered a binary oxidation response, with a threshold around the light saturating point, suggesting two regulated oxidative states of the chl-EGSH. These patterns were not affected in npq1 plants, which are impaired in non-photochemical quenching. Oscillations between the two oxidation states were observed under fluctuating light in WT and npq1 plants, but not in pgr5 plants, suggesting a role for PSI photoinhibition in regulating the chl-EGSH dynamics. Remarkably, pgr5 plants showed an increase in chl-EGSH oxidation during the nights following light stresses, linking daytime photoinhibition and nighttime GSH metabolism. This work provides a systematic view of the dynamics of the in vivo chloroplastic glutathione redox state during varying light conditions.
Bibliographical noteFunding Information:
This research was supported by the Israel Science Foundation (Grant Nos. 826/17 and 827/17) to S.R. The authors thank Avihai Danon, Zach Adam, and Assaf Vardi for critical comments on the manuscript. They also thank Prof. Toshiharu Shikanai, who kindly provided the pgr5 and gl1 seeds for this research, Prof. Wallace Boon Leong Lim, who kindly provided the TKTP-iNAP4 and TKTPiNAPc Arabidopsis lines and Ms. Charis Chan for her help in shipping the seeds, and Daniel Waiger for his help in acquiring the confocal images. Finally, they thank David Pilzer for his support in performing the gene expression analysis.
This research was supported by the Israel Science Foundation (Grant Nos. 826/17 and 827/17) to S.R.
© 2021 The Author(s).